DEVELOPMENTAL REGULATION OF EARLY SEROTONERGIC NEURONAL DIFFERENTIATION - THE ROLE OF BRAIN-DERIVED NEUROTROPHIC FACTOR AND MEMBRANE DEPOLARIZATION

The RN46A cell line was derived from Embryonic Day 13 rat medullary ra phe cells by infection with a retrovirus encoding the temperature-sens itive mutant of SV40 large T antigen. This cell line is neuronally res tricted and constitutively differentiates following a shift to nonperm issive temperature. Undifferentiated RN46A cells express low levels of tryptophan hydroxylase (TPH), low-affinity neurotrophin receptor (p75 (NTR)), and trkB immunoreactivities, but no detectable levels of serot onin (5HT) immunoreactivity. TrkB, p75(NTR), and TPH, but not 5HT, exp ressions increase with differentiation and treatment with brain-derive d neurotrophic factor (BDNF). 5HT synthesis in RN46A cells requires in itial treatment with BDNF, followed by growth under partial membrane d epolarizing conditions. Embryonic raphe cultures treated similarly wit h BDNF and partial depolarizing conditions also demonstrate increased 5HT synthesis. The sodium-dependent transporter for 5HT reuptake is pr esent in undifferentiated RN46A cells, and the apparent K-m and B-max are unchanged by differentiation or BDNF treatment and membrane depola rization. The high-affinity 5HT(1A) receptor is present in both undiff erentiated and differentiated RN46A cells, and while the K-d is unaffe cted by differentiation or BDNF/membrane depolarization, the B-max inc reases 20-fold after differentiation and 3.5-fold further with BDNF un der depolarizing conditions. The expression of the synaptic vesicular monoamine transporter, as determined by the binding of [I-125] iodovin yltetrabenazine, also increases in RN46A cells with differentiation. H owever, 5HT release is constitutive and is independent of acute membra ne depolarization. Collectively these data indicate that distinct aspe cts of serotonin metabolism are differentially regulated during develo pment and suggest that 5HT may function as a developmental signal in a n autocrine loop during early serotonergic differentiation. (C) 1995 A cademic Press, Inc.